The invention relates generally to apparatus and methods for grading or sorting solid objects and more particularly to grading apparatus having a gauging passage between rotating rollers.
Roller graders are used to sort solid objects into different sizes, or grades. Solid objects that are graded include food products, such as fruits, vegetables, nuts, shellfish, portions of meat, poultry, and fish, and non-food products, such as ball bearings, castings, and aggregates. One kind of grader often used comprises pairs of rotating rollers separated by a gauging passage, or grading gap, that increases in width along the lengths of the rollers. A product to be graded, held in the gap by gravity, advances along the lengths of the rollers and falls through the rollers at the position along the length at which the gap widens enough. To prevent the rollers from squeezing the products through the gaps prematurely, the rollers of each pair are rotated about their axes in opposite directions so that the peripheries of both rollers move upward at the gap. In a grader having a planar array of pairs of peeling rollers counter-rotating as described, consecutive rollers rotate in opposite directions across the width of the grader. This means that the right-most roller of the pair and the left-most roller of an adjacent pair, which are separated by a space, both rotate so that their outer peripheries move downward at the space. This downward motion of both rollers prevents the intervening space from being used as a gauging passage. For a grader having, for example, ten rollers (arranged in five pairs) separated by nine spaces, only five gauging passages are formed. Thus, because only a small portion of the potential grading area is available for grading, throughput is limited.